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OFDA 100

Developed with research support from several international organisations, the OFDA is the only image analysis system to be recognised with a Test Method from the IWTO (International Wool Textile Organisation). Since its debut in 1991, the OFDA has become the most common way of automatically measuring fibre diameter distribution, with over 120 in use across 22 countries.

OFDA is used at all stages of the wool processing pipeline, from fleece to yarn and fabric. It is also used to measure other fibres, including cashmere, mohair, alpaca and certain synthetic fibres.

The OFDA is the first automatic instrument to measure fibre opacity and fibre curvature. Fibre opacity directly measures the ability of each fibre to transmit light, and is determined by the fibre's shape, internal structure, colour and surface quality. In white animal fibres, the main cause of opacity is medullation (hollow fibres). Medullated fibres stand out in a cloth since they dye differently.

Fibre curvature is one of the main components of crimp. Several international researchers have had promising results using OFDA fibre curvature measurements to predict crimp, spinning ability and wool bulk (resistance to compression).

Recently, the OFDA has aquired the new feature of measuring the diameter variability along a short length of fibre. This is used to derive a new parameter, the "blob factor". Although this function is in an experimental stage, these values may be the first steps toward an objective measure of fibre cleanliness, and hence a quality control tool for monitoring scouring performance and locating the source of spinning problems.

The OFDA Package

The OFDA package consists of the following components:

OFDA microscope with electronically controlled stage and video image capture circuit board
Sturdy fibreglass carrying case
Automatic spreader to spread snippet onto slides
Guillotine to cut snippets
Monochrome video monitor to display fibre images
40 hinged glass slides, graticule calibration slide, polyester reference slides, instruction manual and sundry accessories
Computer and printer: may be customer supplied, minimum system 486DX2-66, 400MB hard disk, 8MB RAM, MSDos 6.22, mouse, VGA colour screen, Epson FX or HP PCL compatible printer.

Additional requirements

Fibre washing facilities if measuring greasy samples
Conditioned room

Sample Preparation Guide

Advantages and Benifits

There are many advantages to the OFDA over competing instruments. Only two IWTO-recognised instruments automatically provide mean diameter, CV of D and prickle factor measurements, but only the OFDA

improves accuracy because it measures 3000 fibres in the time that others measure 1000.
is the fastest, so you can get more tests done each day.
can routinely measure fibre curve which is a component of crimp that is measurable at all stages of wool processing.
can measure medullation which is the hollowness of fibres that causes dyeing and breakage problems.
does not utilise flammable chemicals that require storage, mixing, and continuous monitoring.
saves time - no regular cleaning of a sump required.
doesn't need to be left running 24 hours per day.
allows you to see the fibres that are being measured.
saves images of fibres: edit or print them using your favourite paint program, insert them into documents, etc.
keep slides of different fibre samples such as wool, mohair, alpaca for re-measuring.
measures up to 300 microns, in case you want to measure exotic fibres such as cashmere.
is portable for demonstrations at different sites - OFDA comes with a fibreglass carry case.
all data can be exported to spreadsheets for further analysis.
can be operated by modem for software support from the factory.
does not require a technician - it can be easily installed by the customer.

You get greater accuracy: Accuracy improves with increasing fibre count. For example, the difference between a 1% prickle factor and a 2% prickle factor with 1000 fibres is only 20 fibres. Fleece Testers, You can obtain a marketing advantage by measuring more fibres and offering fibre curve for the same price

Operating Principles

The OFDA is essentially an automatic microscope set above a moving sample of fibres. The instrument magnifies and captures images of the individual fibres using a video camera, and then identifies and measures each fibre. The fibres and measurement points can be seen on the video screen. A complete measurement cycle on a clean, conditioned sample takes less than 2 minutes. The width of each identified fibre image is measured with a resolution of 1 micron whilst the combined mean diameter and standard deviation are calculated to a resolution of 0.01 micron. After measurement of the requested number of fibres a histogram printout is produced showing the fibre diameter distribution.

OFDA's histogram data include the mean fibre diameter, standard deviation (SD), coefficient of variation (CV), prickle factor (PF) and spinning fineness. The prickle factor is vital to sheep breeders and wool buyers to identify those coarse fibre in a sample that can cause a "prickly" feel in some woolen garments.

If the opacity and curve options are enabled, the OFDA measures these at the same time as it measures the diameter, so there is no extra measurement process involved.

Measurement Images

These images are taken from a normal measurement run of the OFDA. The image on the left is an actual fibre recognition screen; measurement points are shown by lines crossing fibre but actual diameter measurement is made perpendicular to fibre at those points.

On the right is an OFDA image for measuring fibre opacity: the opaque, medullated fibres appear dark. Note that the resolution of these images has been degraded for compression.

Sampling

The OFDA measures 2mm fibre snippets from a clean scoured wool sample. In the case of wool tops or staples, the 2mm snippets are obtained using the supplied guillotine. Wool in scoured greasy core sample or web form is sampled using an optional 2mm minicore machine.

As with all wool fibre diameter measurement systems, for maximum accuracy the OFDA must be operated in a conditioned room, and the fibres conditioned before measurement.

The snippets are spread onto the hinged glass slide in about 30 seconds using the automatic spreader. No mounting liquid is used, and after measurement the fibres are simply vacuumed or brushed off.

Testimonials

Dr. A.R. Edmunds, M.Sc., PhD, FNZEI

I have had personal experience with OFDA continuously since 1991 and have always been impressed with its capabilities, ease of use and reliability. These factors were amongst those that influenced the decision to choose OFDA for use at WRONZ in the extremely wide range of fibre measurement work which plays an essential role in the functioning of WRONZ as the R&D centre for the New Zealand wool industry.

"I know of no other system which is capable of carrying out rapid and reliable measurements of fibre diameter, medullation and curvature virtually simultaneously on the same subsample of fibres and without the need for skilled operators. The linearity and stability of the calibration for fibre diameter are further important attributes unique to OFDA. It has become an indispensible part of the equipment at WRONZ.

Dr Edmunds has been involved in R&D on fibre measurement, especially of fibre diameter, for over 30 years. He participated in all IWTO Technical meetings from 1974 to 1993 and presented numerous Technical Reports on aspects of fibre measurement directly concerned with IWTO Test Methods. Chairman of three IWTO Technical Committee Working Groups, Dr Edmunds contributed to the formation and on-going revision of most IWTO Test Methods and associated Regulations concerned with fibre measurement. He is the world's foremost researcher into fibre diameter measurement using image analysis, and is an assessor of Wool Testing Labs for IWTO, TELARC, and NATA.